The invention described herein was made in the course of work under a grant or award from the U.S. Department of Health and Human Services.
Epithelial diseases (epidermal and mucosal) are a major health problem. Of particular concern are those characterized by abnormal (increased) rates of cell turnover, referred to herein as hyperproliferative epithelial diseases. Examples of hyperproliferative epithelial diseases include psoriasis, cutaneous tumors primary to the skin (basal cell carcinoma, squamous cell carcinoma, melanoma, mycosis fungoides. Bowen's disease), viruses (warts, herpes simplex, condyloma acuminata), premalignant and malignant diseases of the female genital tract (cervix, vagina, vulva) and premalignant and malignant diseases of mucosalf tissues (oral, bladder, rectal). The common diseases within this class are psoriasis and cervical displasia, psoriasis being the most common. Recent estimates have indicated that there are 1 to 3 million persons in the United States with psoriasis, and approximately 150,000 to 250,000 new cases reported annually. The prevalence rate of psoriasis in the United States is between 3% and 4% of the population, with similar prevalence rates in other countries. There is a great need, therefore, for an effective therapeutic regimen.
A variety of therapies are currently used to treat psoriasis including dialysis, chemotherapy (topical and systemic), and photochemotherapy (topical and systemic). Topical chemotherapy is probably the most widely used, employing agents such as tar, retinoids, anthralin, corticosteroids, and antimetabolites.
At present, the most severe cases of psoriasis are being treated with systemic photochemotherapy, which is potentially carcinogenic. Parrish et. al. (1970), Biochem Biophys Acta 217:30, describes the use of oral methoxysalen and long-wave ultraviolet light (PUVA) for the treatment of psoriasis. Clinically, PUVA has remained relatively effective for the majority of patients, while short-term side effects, such as widespread serve erythema, have been tolerable for the severely afflicted patient.
The proposed mechanism for the therapeutic action of PUVA is based on the binding of psoralens to the DNA of the afflicted cells. In this photochemical reaction, psoralen photoadducts with DNA-thymine bases are formed. Psoralan can also intercalate with two DNA base pairs and give intrastrand cross linkages. The inhibition of DNA synthesis and consequent blocking of cell division that results from this photochemical reaction of DNA and psoralen may be the therapeutic mechanism in the treatment of psoriasis.
While the inhibition of DNA synthesis may be the desirable outcome of psoriasis therapy, there is concern that the direct changes in the DNA structure and function by PUVA may have potential carcinogenic and mutagenic effects. It has been reported, for example, that there is an increased pattern of skin cancers developing in patients following PUVA. R.S. Stern et. al. (1979) New England Journal of Medicine, 300:809-813. Thus, while prior art methods of PUVA have shown some promise in the treatment of epithelial diseases, erythema over unafflicted areas of the patient and the potential carcinogenic effect of these treatments make it desirable to develop new therapeutic strategies equally or more effective which do not have potential for such undesirable side effects.
The first report in the literature of the treatment of psoriasis with hematoporphyrin appeared in 1937. The patient was treated systemically with hematoporphyrin and then exposed to ultraviolet light. H. Silver (1937) Archives of Dermatology and Syphilology, 36:1118-1119. Hematoporphyrin has also been reportedly used in photochemotherapy for glioma cells employing visible light. S. G. Granelli et. al., (1975) Cancer Research, 35:2567-2570.
In 1960, Hematoporphyrin Derivative (HPD) was introduced. It is a mixture of hematoporphyrins, such as hematoporphyrin, hydroxyethylvinyl deutero porphyrin, protoporphyrin, and dihematoporphyrin ether. There are probably other porphyrin derivatives included in HPD as well. See R. L. Lipson, The Photodynamic and Fluorescent Properties of a Particular Hematoporphyrin Derivative and its Use in Tumor Detection (Masters Thesis, University of Minnesota 1960); R. L. Lipson et al, (1961) Journal of the National Cancer Institute 26:1-8: T. J. Dougherty et al in Porphyrin Localization and Treatment of Tumors, pp 301-314 (1984). Hematoporphyrins, and in particular HPD, have been studied in recent years for their potential usefulness in both the diagnosis and treatment of malignant disease. The property of selected localization of hematoporphyrins, such as HPD, in animal and human malignant tissues has been exploited for the fluorescent delineation of solid tumors, while the photodynamic action of the compound has been utilized to destroy malignant tissues selectively.
Due to its ability to localize in malignant cells and fluoresce, HPD has been employed in diagnostic methods directed to the detection of malignant tissue. See R. L. Lipson (1960), supra; R. L. Lipson et al (1961), supra; R. L. Lipson et al (1961), Journal of Thoracic and Cardiovascular Surgery 42:623-629; R. L. Lipson et al (1964) Diseases of the Chest 46:676-679; R. L. Lipson et al (1964) Obstetrics and Gynecology 24:78-84; H. B. Gregorie, Jr. et al (1968) Ann Surg 167:827-829. In general, the above diagnostic protocols involve the systemic administration of HPD to the patient, followed by the irradiation of the suspect tissue, with either ultraviolet or visible light, to see if it fluoresces.
The therapeutic potential of HPD for tumors was demonstrated in 1972 when glioma tumors transplanted into rats were destroyed by the combined effect of HPD and visible light. I, Diamond et al (1972) Lancet 2:1175-1177. Since that time, several clinical trials using HPD photoirradiation therapy have been reported in patients with cutaneous or subcutaneous malignant tumors. See. e.g., T. J. Dougherty et al (1978) Cancer Research 38:2628-2635: T. J. Dougherty et al in The Science of Photomedicine. pp 625-638 (J. D. Regan & J. A. Parrish, eds., 1982): T. J. Dougherty et al in Cancer, Principles and Practice of Oncology, pp 1836-1844 (V. T. DeVita Jr., S. Hellman, & S. A. Rosenberg, eds. 1982).
The cytotoxicity induced by HPD appears to result from the intracellular formation of singlet oxygen (a short-lived, highly reactive state of the oxygen molecule) when cells containing the porphyrin are exposed to visible light. K.R. Weishaupt et al (1976) Cancer Research 36:2326-2329. While the exact nature of the cytotoxicity induced by the singlet oxygen pathways is not known, it does not appear to involve the structure and function of DNA directly. The plasma membrane appears to be the main target for cellular destruction in in vitro studies. T. J. Dougherty, "Clinical and Scientific Advances in Photoradiation Therapy" (Porphyrin Photosensitization Workshop, Washington, D.C., Sept. 1981). It has been reported that HPD and visible light cause extensive enzyme inactivation of mouse DNA-dependent RNA polymerase. B. Munson Proc of AACR and ASCO, p 256 (1979) (abstract). Exposure of template DNA to the identical conditions, however, does not cause significant changes in the viscosity or template activity for the RNA polymerases. It was concluded that inactivation of these polymerases is much more sensitive than changes in DNA by HPD-mediated photodynamic action. This suggests the possibility that inactivation of RNA polymerases may be critical in the toxicity to eucaryotic cells caused by this treatment.
Thus there are two possible mechanisms of action that have been found experimentally to be more likely than a DNA interaction, thereby greatly decreasing the change of carcinogenic or mutagenic side effects from therapies based upon HPD.
It has recently been determined that the compound which is active against malignant tissue in the mixture of porphyrins which comprise HPD is dihematoporphyrin ether (DHE). T.J. Dougherty et al, in Porphyrin Localization and Treatment of Tumors, pp 301-314 (1984); T. J. Dougherty (1984) CRC Critical Reviews in Oncology/Hematology 2:83-116. It was determined in these studies that HPD enriched for DHE and administered systemically in a photochemotherapy protocol showed phototoxic properties toward malignant cells. DHE, however, is not the component of HPD responsible for the majority of fluorescence when HPD is used diagnostically. These studies do not report the activity of DHE against nonmalignant proliferative skin disease, or whether it is effective when applied topically or locally.
The above therapies based on hematoporphyrins all suffer from a single significant drawback: they require the systemic administration of the drug. Thus, the patient's entire skin is photosensitized. This whole-body photosensitivity after systemic injection requires that the patient avoid direct sunlight or prolonged contact with bright artificial light for several weeks. If the patient does not avoid contact with such light, widespread and severe erythema can result. Since many epithelial diseases only affect a small and superficial area, it seems unreasonable to treat such patients with a systemic medication and expose them to these side effects. One solution to this problem would be to develop a composition with a photoactive drug which is effective when applied topically. Topically applied drugs provide an ideal method of localizing the effects of the drug, since they need only be applied to the afflicted tissue. Many drugs which act systemically, however, are ineffective in topical formulations.
There is a clear need, therefore, to provide an effective treatment of hyperproliferative epithelial disease which avoids such serious side effects as carcinogenesis, mutagenesis and whole-body photosensitization.